I completed a Glen-l 15 last August. I chose a 5hp Tohatsu. Up to 7hp was recommended but 5 is more than adequate. I chose the 5 because it was as cheap as the 4 and included a external tank (3.5gal). The hull design speed is about 5.5mph. That means that is as fast as it will easily go. It will never plane. The hull being curved at the back prevents that. I find that I seldom use more than 1/4 throttle as any more results in more noise and pushing a lot of water and very little speed increase. The motor is capable of idling remarkably slowly and that is nice for docking. I got it online from a place in Tenessee and they were very good to deal with.
I built my mount out of white oak and it is permanently mounted so that the motor is out of the way when tilted up. I can send pictures if you send an E-mail address. I am at
jeffmckie@gmail.com